This pulls out more functionality from the grammar into simple
c++ source files.

BUG=angle:711

Change-Id: I19121d710dc1543585361cb53a0deb2ea0479db9
Reviewed-on: https://chromium-review.googlesource.com/212938Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Nicolas Capens <capn@chromium.org>